(1)Field of the Invention
This invention relates generally to insecticidal delivery systems, in particular to systems for the delivery of natural entomopathogens to insect-infested loci.
(2)Description of Related Art
Use of natural biological predators to control populations of harmful insects has attracted increasing interest as the shortcomings of chemical pesticides have become more obvious. Despite the uncontroverted success of DDT in practically eliminating malaria as a worldwide scourge and the stunning increases in agricultural productivity associated with the judicious application of pesticides, attention has been increasingly focused on the negative effects of chemical agents.
Living insecticidal agents, delivered under controlled conditions, have narrow host ranges and can control the spread of specific hosts, without affecting natural predators or beneficial organisms. Such agents, herein termed entomopathogens, include bacteria, such as Bacillus thuringiensis, baculoviruses, fungal pathogens, and insect nematodes. These biological insecticides are generally more costly and less persistent than their chemical counterparts. Many entomopathogens are susceptible to rapid environmental degradation caused by exposure to ultraviolet radiation, heat, desiccation, substrate pH, or microbial competition, severely limiting their practical use. Consequently, efforts have been directed to both reducing manufacturing costs and maintaining the conditions necessary for preserving the activity of bioinsecticides to increase their competitiveness versus chemical insecticides.
Encapsulation technology similar to that developed for chemical insecticides has been used to protect and preserve entomopathogens. For example, microencapsulation of nuclear polyhedrosis viruses with polyvinyl alcohol, ethylcellulose, and other polymers has been reported. The microencapsulation of insecticidal crystal spore complexes of Bacillus thuringiensis has also been reported in the form of granules of approximately 500 microns diameter. Polysaccharides such as starch and cellulose have also been crosslinked with borate, calcium or xanthide to produce matrices that can be processed into granules of desirable sizes, densities and porosities. Unfortunately, this encapsulation process is not suited for entomopathogens because the presence of hydrogen peroxide, borate and alkaline pH in the crosslinking process kills the living insecticide.
Insect nematodes (Steinernematidae, Heterorhabditidae, Mermithidae) have been shown to be highly effective bioinsecticides (Poinar, "Nematodes for Biological Control of Insects", CRC Press, Inc., Boca Ratan, Fla., 1979). However, insect nematodes require moist conditions to survive and function. When nematodes are dried they lose activity rapidly; subsequent rehydration fails to restore the lost activity. One method of preserving nematodes in a moist environment is via the microencapsulation processes of U.S. Pat. Nos. 4,615,883, 4,701,326, and 4,753,799. This art microencapsulates the nematodes in calcium alginate. The alginate microcapsules, however, have several drawbacks. They are fairly large and rigid and consequently are not appealing to insects as well as being out of the chewing range of smaller insects. Additionally, the ability of the alginate microcapsules to maintain moisture conditions conducive to survival of the nematodes has also been questioned (Dunkle and Shasha, Environ. Entomol., Vol. 17,120-126, 1988). To reduce the rate of desiccation, others have used water thickeners, mineral oil, or surfactants. See, for example, U.S. Pat. No. 4,178,366. With insect nematodes most of these approaches are ineffective in preserving the moisture content and consequently the biological activity. Some have adverse effects on biological activity or repel the target insects, thereby making them ineffective for their intended purpose.
There exists a need therefore for a low cost, reliable method of protecting entomopathogens from desiccation without interfering with their ability to infect and destroy undesirable insects.